Treatment of isomeric aromatic compounds



Sept. 5, 19.50 l l. F. BROOKE ErAL 2,521,444

TREATMENT' 0F ISOMERIC AROMATIC COMPOUNDS Filed June 28, 1946 3 Sheets-Sheet 1 lu N ln k 0 \'-"Y mgf f Suv-)Af "um, 4 4 k 2 Sept. 5, 1950 L F. BROOKE ErAL TREATMENT oF IsoMERIc mon/:Anc coMPouNns :s sheets-sheet 2 Filed June 28. 1946 @mlm $65 .For

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mersy Patented Sept. 5, 1950 j TREATMENT or rsoMaarc suonano CoMPoUNns .Lloyd F. Brooke, Berkeley Highland Terrace, andv Gordon E. Langlois, El Cerrito, Calif., and Arthur E. Stickland, Mount Royal, Montreal, Quebec, Canada, assiznors to California Research Corporation, 'San Francisco, Calif., a corporation of Delaware Application June 28, 1946, Serial No. 680,156 (ci. 26o-66s) 14 Claims. l

'I'he present invention relates to the treatment of isomeric aromatic compounds and pertains most particularly to the resolving of mixtures of isomeric paraand meta-diallwlbenzenes, especially those' isomeric mixtures which cannot be separated readily by fractional distillation.

Somev isomeric aromatic compounds, such as dialkvlbenzenes, boil at temperatures so close togetherV that separation by fractionation is not practical. For example, para-xylene boils at isomers or a fraction enriched with one isomer may be obtained. The solvent, which may or may not form a loose chemical bond or complex with an isomer is readily recovered for recycle, which ease of recovery permits a simpliied process ow.

Further obiects and advantages of the present invention will be readily apparent from the fol- .lowing description taken in reference to the 28l.03 F. and meta-xylene has a boiling point of 282.39 F.; therefore, mixtures of these two xylenes cannot be readily separated by fractionation. It has heretofore been proposed for the separation of xylene mixtures to partially sulfonate the mixture and then to fractionally crystallize out the preferentially sulfonated product, meta-xylene sulfonic acid, and thereafter to hydrolyze the separated sulfonic acid compound to obtain pure meta-xylene. This and other prior methods have not come into use for various reasons, including low yields, lack of product purity and other disadvantages. i It is, therefore, an object of this invention to provide an improved method of separating isomeric aromatic compounds, which method is simpleand straightforward and permits flexible and -efliicient plant process design.

A particular object of this invention is to provide a simplified method of separating metaand` I paraxylenes by a solvent extraction process.

It is a-. further*object to provide a comiiiuatiinij drawings, wherein:

Figure 1A is a schematic flow diagram of an .embodiment of the separation system of the present invention.

Figure 2 is a schematic flow diagram, illustrating an extract regeneration and isomerizatlon system.

Figure 3 is an alternative combined system shown schematically. y

-In accordance with the present invention, a

mixture of isomeric aromatic compounds .is

thoroughly contacted with a liquid mixture of HF and BFJ, whereby one of the isomers is preferentially absorbed in the HF, BFa liquid; thereafter, the phase of remaining unabsorbed compounds is separated from theenriched solvent; and subsequently, the absorbedisomer is freed from the HF, BF: solvent phase.

The present process is preferably applied to the separation vof xylenes. Thus, from -xylene mixtures meta-xylene is preferentially absorbed in the HF, BFs liquid, ortho-xylene being sepa- .rated by fractional distillation before or after extraction and isomerization process.v wh,ereilt.y either the extracted or vunextractedv isomer isomeriz'edfto yield a mixture fromv'whichffu'r'- therfquantitiesjof the desired isomer are sepa-` V'rate fishy.wsolvent extraction. By means 'of this combination of steps a mixture of.. -isom'eric xylenes may be substantially completelyconvertedto the desired isomer. 1 l

v Itfis also an object *of this invention to p ro-f vide a method fresolving mixtures of isomerlcaromatic compounds into their constituent isoby means of va liquid mixture ofjI-IF' and g By ans ofthe process of the vpresent inven- 'V ich involves the' solvent extraction of lxtures, with a liquid,v mixture of HF `Bf ,f -asimple and improved separationof isomeric constituents is readily and inexvely obtained. By varying the proportions r mandara in their mixture, as wen as me ratio of-"said HF, BFa Virxixture to aromatic compounds being treated, either substantially pure 55 be treated are substantially completelyvaromatic rpm'atic compounds, ysuch as isomericr treatment of the xylene mixture'with HF, BF:

liquid. While separation of xylenes constitutes the preferable and lespecially advantageous application of the present process, -benecial results and "some of the advantagesof the present invention will be .obtained when the present process applied to the separation of mixtures of other lsomeric dialkyl aromatic hydrocarbons, such as v diethylbenzenes; ethyltoluenes. methyl propyl benzenes, methyl isopropyl benz'enes, etc., or other isomeric aromatic compounds such as.

cresols, etc.

Commercial fractions ofA isomers may be used as a feed'material in the present process. For example, xylene fractions from petroleum sources, coke-oven light oil, drip oil or the like may be advantageously treated. Suitable fractions of isomeric aromatic compounds may be obtained from mixtures byfractional distillation and/or extraction lwith solvents capable of eieeting a separation of aromatic compounds from parafflnlc hydrocarbons. Preferably, the fractions to compounds and especially closely-boiling fractions of isomeric aromatic hydrocarbons. Such compounds when associated with non-aromatic compounds, such as paraftlns, can be obtained as pure aromatic mixtures by treating with solvents to substantially completely dissolve the aromatic compounds, and subsequently freeing the aromatic compounds from the solvent in a separated extract phase. Thus, a fraction containing the isomeric aromatic compounds and non-aromatic compounds may be treated with such solvents as liquid SO2, furfural, aqueous phenol, liquid hydrofluoric acid with boron fluoride, and the like. It is especially advantageous to employ liquid mixtures of HF and BF: under conditions, including a high ratio of said liquid mixture to aromatics, to dissolve substantially all the aromatics from said fraction, since by correlating the temperature, contact time, proportion of subsequently added selectivity promotor, such as a. low-boiling n-paramn and the like, with an intermediate partial separation of HF and BF3 from the primary extract, a cyclical interdependent process including the steps of preferential extraction of an isomeric aromatic compound or compounds can be effected.

On the other hand, a fraction containing isomeric aromatic compounds and non-aromatics can be treated in accordance with the present invention to preferentially absorb an aromatic isomer or isomers, leaving a mixture of aromatics and non-aromatics in a rafdnate, and subsequently separating said raffinate with a solvent under conditions to effect substantially complete dissolution of said remaining aromatic compounds.

Suitable mixtures of isomeric aromatic compounds may be prepared in various ways, such as by catalytic alkylation of aromatic compounds with oleflns, e. g., ethylene, propylene, butylene, etc. Especially effective in combination with the preferential extraction steps is alkylation of an aromatie compound with an olefin by means of a mixture of HF and BFs under suitable conditions. Thus, for example, HF, BFa can be used to catalyze the alkylation of toluene with propylene toproduce a mixture of cymenes, which mixture without removal therefrom of the HF, BFs alkylation catalyst can be separated into its component isomers by correlating the ratio of cymenes to HF and BFs in liquid form in accordance with the preferential absorption steps herein described.

In some cases, it will be more efficacious to prefractionate the isomeric mixtures, whereby a separation of one isomer from the remainder may be obtained; in other cases, it may bemore convenient or desirable to separate one of the products of HF, BFa treatment into its components by fractional distillation. Thus, a xylene oil containing al1 three xylenes may be rst fractioned to separate o-xylene, whereby there is obtained a mixture consisting primarily of metaand para-xylenes along with some impurities such as ethylbenzene, which mixture may then be treated with liquid HF, BF: to preferentially absorb m-xylene. In this manner, substantially pure m-xylene can be obtained from the extract phase and substantially pure p-xylene from the rainate phase. Also, a broader boiling range xylene fraction containing all three xylenes may be first treated with HF, BFs to absorb metaxylene, and the raiilnate therefrom fractionally distilled to separate or concentrate the ortho and para-xylenes.

Although the process can be beneficially used to treat isomeric aromatic mixtures generally, the present invention will be hereinafter specifically referred vto the preferred xylenes as illustrations for purposes of clarity and simplicity only.

The liquid mixture of HF and BFs, which acts as the solvent or absorbent, may contain from about 1% to 70% by weight of BFs, depending on other conditions of temperature, contact time, and amount of solvent, and whether simultaneous isomcrization is desired. Ordinarily, from l0- 50% BF: in the liquid HF, BFg mixture is preferred for preferential absorption of m-xylene from xylene mixtures. The amount of liquid HF, BFa mixture employed is at least sufficient to form' two phases on settling. The ratio of HF, BF: liquid to aromatics is equal to or less than that at which the preferentially absorbed aromatic isomer is substantially completely soluble in the HF, BFs liquid. Ordinarily, only sufficient HF, BFs liquid is employed to extract no more than a'bout 95% of the preferentially absorbed isomer. In the countercurrent or plural stage extraction systems, this limiting factor may be lsomewhat exceeded near the raflinate end of the system in order to 'obtain, for example, high purity p-xylene from ay mixture of pand m-xylenes. However, the point of complete solubility of p-xylene, for example, should not be approached too closely; i. e., less than, and usually appreciably less than, the amount of HF, BF: which would substantially completely dissolve both pand m-xylenes should be used.

It is ordinarily preferable to carry out the preferential absorption in the presence of a selectivity promoter or solvent modifier. Suitable agents for this purpose are lower normal parailins, e. g., propane, butano, pentane, etc., which are preferable, or higher normal parafllns, isoparamns, naphthenes, or mixtures thereof. Sometimes alight naphtha may be satisfactory. Generally, these added agents are substantially inert under the conditions of preferential absorption.,

lower temperatures, etc., being used with the more reactive compounds to avoid substantial reaction thereof or absorption in the HF, BFa liquid. Especially preferred are the modifiers which boil below, or at least different from, the boiling range of the aromatic compounds being separated. In cases where the added selectivity promoters boil in the range of the aromatic compounds being separated, the railinate resulting fromA the preferential absorption may be treated with a solvent, preferably HF, BFs liquid, under conditions to completely dissolve the remaining aromatics in the raflinate to separate said aromatics from the non-aromatic selectivity promoters.

These promoters are used in limited amounts to increase the selectivity of the preferential absorption. Generally a ratio of about 5:1 or less, depending on the conditions employed, between the promoter and aromatic compounds is the maximum, and a ratio of about l to 2.5:1 is preferable.

When using a selectivity promoter. as is preferable, the maximum ratio of HF, BF3 liquid to aromatics will depend, in'part, upon the nature of the promoter and the amount present, a higher maximum ratio generally being permissible with the larger amounts of promoter. Also, this ratio will depend upon the composition of the HF, BFa liquid and the amount of preferentially,

absorbed isomer present in the feed. For example, in continuous countercurrent extraction of an equilibrium mixture of xylene isomers in the presence of a selectivity promoter, the maximum ratio of HF, BF; liquid to aromatics will be usually on the order of about 3-4:1, a ratio of about 2-3 being most desirable; and in the absence of a selectivity promoter, the ratio of HF, BF; solvent to aromatics is kept below about 1:1, and preferably below about 0.5:1. However, in all cases this ratio should not greatly exceed that value at which the preferentially absorbed isomer is substantially completely soluble in the HF, BF; solvent. On the other hand, sufficient HF, BF; liquid is used to obtain a liquid HF, BF; phase on settling, for example, by using a ratio above about 0.1:l.

In plural stage systems, both the ratio of HF, B115 liquidy to aromatics and the ratio of solvent modifier to aromatics may be advantageously varied as between the stages to increase the selectivity of absorption and/or the purity of railinate or extract phase. Likewise, in column extraction, either concurrent or countercurrent,

multiple injection of HF. BF; and/or selectivity promoter together with rainate and extract recycles may be used. Pressure variations between the absorption zones may also be employed.

The temperature at which the contact between the aromatic compound and the liquid HF, BF; mixture is carried out will ordinarily range from about 0-150 F. more or less, depending upon the proportion of HF and BF; in their liquid mixture, the amount of solvent employed, the contact time, nature of the aromatic compound, the result desired, etc. Where a minimum of side reactions are desired, the lower temperatures such as 30-80 F. are generally preferred. Cooling may be desirable since heat is evolved by absorption of Xylenes in HF, BF; liquid. Suilicient pressure is employed to maintain the HF in liquid form and the desired concentration of BF; in the HF, BF; liquid. Since the total amount of BF; introduced into the absorption zone depends upon the equilibrium pressure of BF; at the temperature employed, the ratio ofl liquid HF, BF; to aromatics, and the gas space above the liquid mixture, suilicient pressure, such as 100-400 lbs. per square inch of BF;, is used to maintain the desired concentration of BF; in the liquid HF, BF; mixture. For example, a total of about 56.6% BF; based by weight on the HF, BF; mixture y was introduced into a contactor under about 345 lbs. per square inch total gauge pressure and containing 1.68 liters of liquid at 100 F. and 3.12 liters of gas space at 120 F., giving a BF; partial pressure of about 278 lbs. per square inch absolute and about 43 weight percent of BF; in the HF, BF; liquid.

'I'he isomeric mixture is contacted with the liquid HF. BF;, preferably with vigorous agitation, for a sufcient period to attain the desired extent of absorption in the solvent. The contacting may suitably be carried out batchwise or continuously or in several stages, and for this purpose combinations of mechanically driven agitators., such as turbo mixers with settlers used either singly or in series or parallel, columns adapted for countercurrent or concurrent iiow, coil reactors fitted with mixing jets, or the like, may be used. Since desirable short contact times are attained by thorough contact, it is preferred to use contacting devices, such as turbo mixers or other relatively high speed agitator and baiile arrangements, wherein the HF, BF; liquid is quickly and finely dispersed throughout the aromatic compounds. Contact time, in correlation with other conditions including thoroughness of contact, will generally range from about 1 minute to 1 hour, more or less; for xylene separations,

using vigorous agitation and mild temperature,

) period of 1 to 30 minutes is usually satisfac- The extraction is carried out under substantially anhydrous conditions and for this purpose dry feed and solvent are used.

After the absorption step and separation of the phases formed on settling, the raflinate or unabsorbed phase, as well as the extract phase or enriched solvent, is treated to remove HF and BF;

l from the aromatic compounds. This removal may be brought about, particularly with the raflinate, by -pressure reduction and/or heating or Aby stripping with an inert gas such as a gaseous paraflin, e. g., ethane, propane, etc., nitrogen, CO2, etc. Preferably, easily-condensible gases, such as propane, rbutane, and the like are employed to facilitate the subsequent separation of HF and BF; from the stripping medium. To remove HF and BF; from the extracted or absorbed aromatic compounds, it is sometimes necessary to apply heat thereto in order to break the loose chemical complex formed between the HF and BF; and the aromatic compound.

After a'bsorptive separation through one or more stages, the railinate or extract may :be further treated, such as by recycle through at least one contacting stage, which may be operated in the higher end of the temperature range, whereby the liquid HF, BF; simultaneously acts as an isomerization catalyst to -produce more of the depleted isomer or isomers. Alternately, for the same purpose, there may be interposed in the recycle stream a separate isomerization stage, using as an isomerization catalyst: HF, BF; mixtures or other suitable catalytic agents, such as aluminum chloride, aluminum chloride-HC1 mixtures, solid phosphoric acid on kieselguhr catalysts. It is an especially advantageous feature of the present invention to combine with the preferential absorption steps an isomerization of the unwanted isomer or isomers by means of HF, BF; mixtures. Particularly eiective is the combination of recycling the unwanted isomer or isomers to a simultaneous isomerization and selective absorption stage employing an HF, BF; liquid under isomerization conditions. Suitable temperatures for isomerization generally range from about 125 F. to about 250 F. or more; depending in part upon the compound -being isomerized; the lower temperatures consistent with the extent of isomerization desired are preferred. For example, when it is desired to obtain m-xylene as the main product, an isomeric xylene mixture may be contacted with liquid HF, BF; at a temperature of about F-225 F., whereby p-xylene and, if present, o-xylene, including that recycled from the raflinate obtained from the absorption, are isomerized to produce m-xylene. For the same purpose of obtaining m-xylene, the absorption of m-xylene in HF, BF; liquid may be carried out at low temperatures, such as 30-80 F., and the pand'o-xylenes remaining in' the raflinate isomerized in a separate zone :before recycle yto the absorption step. Thereby substantially complete conversion to m-xylene may be obtained. In a like manner, por o-xylene may be the main product -by recycling the undesired xylene isomers.

The practice of the present invention and its Y respectively).

there have been omitted from the drawing certain details such as pumps, valves, pressuring means, coolers, heat exchangers, etc., as will be readily supplied by one skilled in the art. It is also evident that the materials forming the treating apparatus, especially that portion in contact with large concentrations of HF and BFs, is preferably substantially inert,'such as Monel, nickel, Hastalloy, etc., so that no reaction of HF and/ or BFi takes place with the apparatus material to form excessive amounts of contaminants or substances inhibiting the carrying out of the present process.

Referring to Figure 1, the separating system comprises a series of contacting stages I, 2, 3, l, l and 6, together with their respective settlers II, I2, I3, Il, I and I6. suitably, each contacting stage may be a turbomixer. A dried feed material such as a xylene oil containing all of the isomeric xylenes is introduced through line 26 into stage #L Preferably, a diluent or selectivity promoter, such as liquid pentane', is also introduced in to stage 'I along with the xylene feed. Simultaneously in the continuous system, a liquid HF, BF: of the desired composition is fedthrough line 2l into 'stage I at a rate giving a proper ratio to the xylene mixture, such as about 1.5:1 volume ratio. Where no appreciable chemical reaction such as isomerization is desired the temperature may be maintained at about 3c-80 F., such as for example at about 70 F.

After a'contact time of about 15 minutes i stage I at this temperature, the diphasic mixture is withdrawn through line 22 into a settler II, wherein a separation of the phases takes place. The separated heavier HF, BF3 liquid or extract phase is withdrawn through line 23 for subsequent removal of HF, BFa therefrom to `yield a xylene fraction enriched in the preferentially absorbed isomer, such as m-xylene. The separated upper hydrocarbon phase containing the selectivity promoter, when used, is passed through line 25 to contacting stage 2.

The feed into stage 2 may contain in addition to the first stage rafnate the extract phase from the succeeding stage 3 via line 26 and further quantities of HF and/or BF; through line 21, if desired to obtain optimum HF, BFa liquid composition and ratio to xylene. The eiiluent from stage 2 is conducted through line 28 to settler I2 and therein is separated into railinate and extract phases which are withdrawn through lines 29 and 30, respectively. When feeding an equilibrium mixture to stage I, it is preferable not to introduce also second stage extract into the first stage but rather to discharge said second stage extract via line 30 for removal of HF and BF3 to produce an enriched fraction. Under different circumstances, however, the second stage extract may be brought into the rst contacting stage I. In such case and others, it may be more desirable to introduce the feed material to the separation system at an intermediate stage.

In a manner similar to stage 2, the feed to each of stages 3, l, 5 and 6 will comprise the raflinate from the preceding stage (via lines 29, 35, 36 and 31, respectively), the extract phase from the succeeding stage except the last stage 6 (via lines 40, 4l and 42 respectively) and, if desired, makeup HF and/or BF: (via lines 45, 46, 41 and 48, Eilluent lines 5I, 52, 53 and 56, respectively, are provided to discharge from the contacting stages 3 to 6 to their respective settiers I3 to I6.

The iinal raffinate withdrawn from settler I6 through line 55 will contain the'paralnic selectivity promoter, which can be subsequently removed, and will be substantially free of the preferentially absorbed isomer, e. g., m-xylene.

Referring to Figure 2 oi' the drawings. for suitable combination with the separation system, there may be provided a prefractionator 60 into which, for example, the final raillnate from line 55 (Fig. 1), may be fed through line 6I. Therein selectivity promoter, such as liquid pentane, if present, and residual HF and BF: together with low boiling aromatics such as benzene and toluene may be separated from the desired aromatic compounds and withdrawn through line 62. This stream may be desirably recycled to the separation system and may be introduced, for example, through line 20 with the feed to contacting stage I. From the fractionator 60 the remaining aromatic compounds may pass through line 63 to 'a rerun still 64, wherein, in the case of xylene mixtures, substantially pure p-xylene may be taken overhead as product through line 65, and o-xylene withdrawn through line 66.

This o-xylene stream may be combined with other undesired xylenes, such as, for example, a m-xylene fraction from conduit 61, and, if desired, other xylene mixtures from line 68 to form a, combined xylene feed to isomerization contactor 10. Recycle HF. BF: from line 1I together with fresh HF and/or BF; via line 12 is introduced into the contactor 16 to provide the catalyst for the isomerization. Suitable conditions, such as a temperature of about 200 F., a contact time of about 15 minutes, and suiilcient agitation, as may be provided by using a turbomixer or the like as the contactor, are maintained in the contactor 10 to obtain the desired isomerization. Discharging via line 13, the diphasic mixture of isomerization product and HF, BFs liquid is separated in settler 15, the HF, BF; liquid being recycled in part, if desired, as indicated. The whole (as shown) or only part of the isomerization product may be passed through line 'I6 to a. fractionator 11 for removal of the small amount of heavier compounds formed during isomerization. These heavier compounds are withdrawn as bottoms through line 18, and th'e overhead, which may be an equilibrium mixture of the isomeric xylenes, withdrawn through line 19 for use as feed to the separation system shown in Figure 1.

Part of the HF, BF: liquid separated in the settler 15 from the isomerization product and which liquid may contain absorbed xylenes, depending in part upon the composition of said liquid, may be taken through line 83 andcombined in line 84 with other extract phases, such as those obtained from lines 23 and 30 in the system of Figure 1, to form a feed stream to an HF, BF; regenerator 35.- Suitable conditions, including temperatures and pressures as low as possible, are employed in the regenerator 85 to obtain substantially complete removal of HF and BF: through line I6. The remaining aromatic compounds, e. g., xylenes which are predominately m-xylene, in the arrangement indicated, may be passed to the isomerization contactor 'l0 through line 61 as mentioned hereinabove.

It will be readily apparent that various modiications and/or changes lin the above-described illustrative treating system may be made without departing from the spirit of the present invention. Thus, instead of six contactors in series, as shown, one or more contactors and as high as eight to ten contactors in series of the same or different types may be sometimes' advantageously used. Further, as indicated hereinabove. the, contactors may be operated at higher temperatures or with varied percentages of BE in the liquid HF, BF: solvent whereby in addition to absorption there is simultaneously obtained an isomerization of the xylenes.

By way of illustration of the combined systems of Figures 1 and 2 and any part thereof, the following is given:

A xylene mixture containing 17% o-xylene,

63% m-xylene, and 20% p-xylene (percentages.

are by volume) at a rate of 4460 B/D (barrels per day) and liquid n-pentane at a rate of 11130 B/D are introduced through line 20 into contacting stage I. Simultaneously 4470 B/D of anhydrous hydrouoric acid and 620,000 lbs. per day of boron fluoride are introduced into stage I, and substantially the same amounts of HF and BF: together with 1737 B/D of extract are withdrawn from settler I I through line 23.

Ralnate from rst stage settler II is passed through line 25 to stage 2 at a rate of 2723 B/D of xylenes in addition to n-pentane. Make-up HF, BFa mixture is introduced through line 21 at a rate of 630 B/D of HF and 93,000 lbs./D of BFa. Discharging from second stage settler I2 through line 30 is 4340 B/D ofHF, 550,000 lbs./D of BFa, and 1540 B/D of extract.

The rates of ow in the remaining streams in the subsequent stages are as follows:

Rainates (Wlene portion) The compositions of the various xylene fractions in the rafnate and extract phases from each stage are given in the following table:

Composition, volume percent Stage 1 2 3 4 5l 6 Raliinate:

o-xylene 24.6 25.4 27.2 30.4 40.8 44.8 m-xylene 48.7 44.7 40.7 33.8 20.0 2.5 p-xylene 27.7 29.9 32.1 35.8 43.2 52.7

Extract:

oxylene 6.7 7.1 7.5 8.0 9.1 13.8 m-xylene 85.5 84.6 83.7 82.5 79.5 70.0 p-xylene 7.8 8.8 8.8 9.5 11.4 16.2

The final raffinate from line 55 (Fig. 1) may be introduced at the same rate, through line 6| are taken overhead through line 62 for recyclel to contacting stage I. The bottoms taken through line 63 to rerun still 64 are separated.

into an overhead stream of 650 B/D of 95.2% p-xylene and a bottom stream of 530 B/D of o- Xylel'le'.

The m-xylene enriched extract phases from lines 23 and 30 (Fig. l) may be combinedinto a stream consisting of 3277 B/D of 85.1% m-xylene, 9110 B/D of HF and 1,170,000 lbs./D of BFz, which stream forms via line 8l (Figi 2) part of the feed to regenerator 85. Therein the HF and BFs are substantially completely removed from the extract phase, leaving as bottoms in line 61 a m-xylene enriched fraction which is combined with the above-mentioned o-xylene stream and, if desired, for example. 652 B/D of fresh xylenes (via line 68) of the same composition as in line 20 (Fig. 1). This combined xylene mixture is introduced into isomerization contactor 'I0 under the following conditions: 0.3 vol. HF per volume of xylenes, 0.03 part by Weight of BFa per part of HF (as charged), 15 minutes contact time, and 200 F. l

The resulting isomerized mixture and HF, BF: liquid are separated in settler '15, from whence 4460 B/D of equilibrium xylenes as raflinate through line I6 may be fed directly to separation stage (Fig. l). The separated HF, BFs liquid phase may be partly recycled together with fresh HF and/or BFa to contactor 'l0 and partlyto regenerator 85 as indicated.

In Figure 3 is shown an alternative arrangement of a complete system, including feed preparation,

preferential extraction, and isomerization. Therein a dried mixture of isomeric aromatics and parailins from line |00 are combined, if desired, with a liquid diluent such as propane from line |0|, the diluted mixture in line |02 being mixed with HF, BFa liquid via line |03 to serve as feed to an extraction zone |04. Therein a substantially complete separation of aromatics from paralns is obtained, the aromatics being withdrawn via line |05 in an extract phase, and the paraflins remaining undissolved as raffinate in the eflluent line |06. When a diluent such as propane is used, the rainate is passed to a propane recovery column |01, whereby propane is recycled through line |0I and parailns discharged through line |08.

The HF, BFa liquid solution of aromatics in line |05 may be combined with other extract phases, such as via line ||0, and then passed through line III to a solvent regenerator ||2, wherein HF, BF; taken overhead is recycled after condensation (not shown) partly through line |03. The remaining aromatics issuing from regenerator I|2 through line ||3 may be combined with other extracted aromatics, such as via line I |4. This mixture may be all (as shown), or only partly, fractionated to remove higher and lower boiling impurities. For example, in case of isomeric xylenes, the mixture may be passed through line I I5 to a column I6 in which Css and heavier are discharged as bottoms through line ||1. The overhead material passes through line ||0 to a second fractionator I9 for removal of the lighter boiling materials, such as Cvs through line |20. The bottoms in line |2| comprise the purified isomeric xylene feed to the isomerization and preferential absorption parts of the system, which feed may be purified and prepared in other ways.

Due to the addition of extracts via lines ||0 and anche 1l Hl, this mixture is enriched with m-xylene.

A (For clearness, the xylenes will be used hereintacted with a suitable catalyst such as HF, BF:

liquid introduced via line |26 and under conditions conducive to produce an equilibrium mixture of the xylene isomers. The reaction mixture vis led through line |21 to a settler |28, wherein the liquid HF, BFS is settled out and withdrawn through line |23. Part of the I-E. BF: is recycled through line |26 to the isomerlzation contactor and part is passed through line |30 to an HF, BFS regenerator |3 HF, BFS is taken overhead from regenerator |3| and recycled through line |32 to isomerization contactor |25. The bottoms from regenerator |3| forman extract passing through line lida and line iid into the Cn removal column H6.

The upper phase in settler |20 comprises an equilibrium mixture of xylene isomers and is passed via line |35 to a series of preferential ex- -traction stages after admixture with a selectivity promotor, such as liquid propane, via line |36. The propane-xylene mixture passes through the extraction stages III, |42, |43, and |44 countercurrent to liquid HF, BFg solvent entering through line |45. Ordinarily three stages will be sufcient for complete separation of meta-xylene from paraand ortho-xylene; however, since a fourth stage would probably be provided in a plant for safety, four stages are shown here. The final extract-mainly meta-xylene--passes through line ||u to the HF, BFz; regenerator; the final raiiinate passes through line |45 to a propane recovery column |41, from which propane is recycled through line |36 and appropriate condensers (not shown). The remaining propanefree mixture of orthoand para-xylenes is taken through line |48 to a column i60, wherein substantially pure para-xylene is taken overhead through line ISI and substantially pure orthoxylene is discharged through line |22 as bottoms.

In the above description of Figure 3, many variations may be made; the representation is schematic; and various details such as condensers. etc., will be readily supplied by one skilled in the art. For example, with some isomeric aromatic compounds, such as cymenes, HF alone may be used as the isomerization catalyst.

To illustrate further the present invention, several experiments were carried out in a Monel stirrer, to which the reactants were charged in batch. After the desired contact time at a controlled temperature, the mixture of aromatic compounds and HF, BF3 liquid was withdrawn and allowed to stratify. The lower HF, BF: phase was diluted with water and extracted with pentane. The pentane extract was water washed and the pentane removed by distillation. The rafilnate and extract, aswell as a composite product obtained by combining the portions of the railinate and extract in the ratio of their volumes, were fractionated and the cuts therefrom subjected to ultra-violet analysis.

Example A.A xylene charge oil was contacted with a liquid HF, BFa mixture containing 43 12 weight percent BF: and the remainder HF at 100' F. for 15 minutes. The volume ratio oi m', B115 liquid to xylenes was about 1.5:1. Isobutane was added at a volume ratio to xylenes o! 2.4: 1. There 5 was obtained 39.1 of stabilized (isobutane-free) rafiinate and 52.5% of extract, based by volume on the xylenes charged. The results were as follows. wherein the values are on the basis of volumes per 100 volumes of xylenes charged and corrected to 100 recovery:

Cum imo 0ilu l5 Components Charge posite agg; Extract extlrlaclt to Product isomer in miilnate P 5. 6 4. 9 0. 7 2. 0 1. 7 0. 3 it eavier Hydrocarhms 20.3 3.8 16. 5

Example B.-Another xylene oil was contacted with a liquid HF, BF: mixture containing l39 weight percent BF: at 70 F. for 5 minutes with a volume ratio of HF, BF: liquid to xylenes of about 80 38.2 volume percent extract, as follows (the values having the same basis as in Example A):

Example C'..-At a volume ratio of HF, BF: liquid to xylenes of 0.511, a xylene oil was contacted 50 for 15 minutes at 100 F. with a liquid HF, BF:

mixture containing 37 weight percent of BFa. 'I'he results follow (the same basis being used as in Example A):

Com islatio oliti Components Charge posits Extract extrmelt Prodr um 130112311? Eth lbenzene 2. l 2. l l. 6 0. 5 o-xy ene 3. l 4. 7 8. 1 l. 6 0. 52 mxyylge lg 72g 60. 8 25. 6 0. 60 eavi} r 6. 11.5 3.1 0.27 carbons..... 2.4 1.0 l. 4

Example D.-A liquid mixture containing 49 weight percent BF; and the remainder HF was y used to treat a xylene oil in a volume ratio of 1.9: 1

for 15 minutes at 100 F., in the presence of npentane in a volume ratio of xylenes of 2.5:1. The pentane-free rafilnate obtained amounted to 31.0 volume percent and the extract 45.6 volume 75 percent, based on the charged xylenes. The an- 0.5:1, yielding 49.9 volume percent raillnate and y alyses follow (the basis'belng the same as in Example A):

Ratio of C t Ch Colin RB" F r f Mimet? om nen s arge pos Y rm' ex rac o po Product amm somer in railinaie 14. 5 7. 9 4. 8 3. 1 0. 64 46.2 46.4 6.8 39.6 5.81 -xy 24. 8 15. 9 12. 8 3. 1 0. 24 heavier Hydrocarbons 14. 6 0. 9 13. 7

Example E.For 15 minutes at 100 F. a. xylene oil was contacted with a liquid HF, BFa mixture containing 26 weight percent BF: in a volume ratio of HF, BF: liquid to xylenes of 0.5:1. whereby 77.1 volume percent of rafiinate and 16.2 volume percent extract, based on xylenes charged, were obtained. 'I'hese analyzed as follows (the values having the same basis as in Example A) Ratio of c t Clar 001122 Raf' EX isotmerzi? omponen ge pos ex rac o Prodmate met isomer in uct railnate Ethyl'honvpno 2, 1 93. 2 80.1 72. 2 7. 9 0. 11 4. 16. 1 8. 9 7. 2 0. 81 xylene 0. 7 r1. 8 1. 6 0.2 0. 13 eaver hydrocarbons 2. 2 0. 0 2. 2

Example F.-A xylene oil was contacted with a liquid HF, BFa mixture containing 27 weight percent BFa at 76-78 F. for 5 minutes with a voiume ratio of HF, BFa liquid to xylenes of about 1.3:1 and in the presence of 2.5 volumes of liquid propane per volume of xylenes. The total gauge pressure was 236 lbs. per square inch. The results were as follows (in this and the following examples, the values given are based on 100% recovery and are percentages by volume of each product):

Com- Chargc posite Railinate Extract Product Vol. Per Cent of Charge- 62. 9 1 Components: i

Tnlnann O. 2 0, 6 Ethylhen une, 0. 3 0. 5 o-xyleno 18. 4 18. 0 24. 6 6. 8 11i-xylene l 60. 1 56. 9 4l. 1 83. 7 xylenc 21.5 23.3 33.8 5.5

eavicr hydrocarbons 1. 3 3. 4

It will be noted that there can be separated by distillation from the above extract a fraction containing 94 parts of m-xylene and 6 parts of p-xylene.

Example G.-A xylene fraction was treated with an HE', BFa liquid containing 30 weight percent of BFa for 5 at 75-78 F. in the presence of 2.5 parts of liquid propane per part of xylenes under a total pressure of 218 lbs. gauge. The ratio of HF, BF: liquid to xylenes was 13:1. The treatment gave the following results:

cna Coliti- Ramna E rg@ POS e. te xtract Product Voi Per Cent of Charge-- 59. 3 40. 7 Components:

Toluene 0. 1 Ethylbenzene 0.1 o-xylcne 10. 2 10. 9 15. 4 4. 4 m 79.1 75. 4 66.0 89.0 xylene. l0. 6 12. 2 18. 6 2. 9

eavier hydrocarbo 1. 4 3. 4

A fraction containing 97% m-xyiene and 3% p-xylene can be separated from the extract by fractional distillation,

Example H.A xylene mixture was extracted with an HF, BFs liquid containing 21 weight percent of BF: at a. ratio of HF, BF: liquid to xylene of 1.2:1 and with 2.5 volumes of added liquid propane per volume of xylenes under a. pressure of 315 lbs. per square inch gauge for 5 minutes at Fractions separated by distillation from the extract and raflinate may contain 86% m-xylene and 14% p-xylene, and 4.9% m-xylene and 95.1% p-xylene, respectively.

Example I.-A mixture of 1 volume of xylenes and 1 volume of liquid n-pentane was thoroughly contacted for 5 minutes at 75-77 F. with 0.7 volumes of HF, BFaliquid containing 26 weight percent of BFa and under 149 lbs. gauge pressure,

yielding the following results:

Com- Charge posite Raflnatc Extract Product Vol. Per Cent of Charge.- 72. 3 27. 7 Components:

n none 0. 1 0. Ethylbenzene- 0. 3 l. g 0xylcne 18. 4 18. 2 23. 2 5. 3 11i-xylene- 60. 1 58. 8 49. 0 83. 9 gxylene 2l. 5 22. 3 27. 8 8. l

eavier hydrocarbmw 0. 3 1. 1

Example J.A mixture of 1 volume of xylenes and 1 volume of liquid n-pentane was thoroughly contacted for 5 minutes at 'I4-78 F. with 0.8 volumes of HF, BF: liquid containing 48 weight percent of BFS and under 322 lbs. gauge pressure, yielding the following results:

Com- Charge posit-e Raiflnate Extract Product Vol. Per Cent oi Charce 61. 6 38. 4 Components:

Toluene 0, 3 0, 9 Eth lbenzene 2. 4 3. 9 o-xy cne 18. 4 16.0 21. 8 7. 0 m-xylene- 60. l 58. 5 43.6 82. 6 Eixylene 21. 5 22. 4 31. O 8. 5

eavier hydrocarbons 0. 4 l. 0

Example K.A xylene fraction was treated with an HF, BFa liquid containing 35 weight per cent of BFa at a ratio of HF, BF3 liquid to xylenes of 0.7:1 for 5 minutes at 7678 F. under 238 lbs.

gauge pressure. With one volume of liquid propane per volume of xylenes present, the results were as follows:

Example L.-A xylene fraction was treated lwith an HF, BFa liquid containing 34 weight per cent of BFa at a. ratio of HF, BFa liquid to xylene of 0.7:1 for 5 minutes at 'I6-78 F. under 278 lbs. gauge pressure. With 2.5 volumes of liquid propane per volume xylenes present the following results were obtained:

Example M .-A mixture of xylenes was treated at 31-35" F. for 5 minutes under 115 lbs. gauge pressure with an HF, B'Fa liquid containing 33 weight per cent of BFJ. With 1.4 parts by volume of HF, BFs liquid and 2.5 parts by volume of liquid propane per volume of xylenes, the results were as follows:

Oom- 'Charge posite Rafnate Extract Product Vol. percent ol Charge.-- 47. 0 53.0 Com nents:

ninnnn 0, 1 0, 2 Eth )benzene 0. 1 0. 5 l. l 0- elle 18. 3 17. 0 28. 7 6. 7 m-xyiene--- 60. 3 57. 7 28. 7 83. 4 -xylene 21. 3 23. 6 41. 5 7. 7 eavier hydrocsrimn 1. l 2. 0

In comparing'tlie elect of decreased temperature from that used in Example F, it will be comnoted that an increased absorption is obtained Charge Pgooit mute xmct without appreciably changing the selectivity.

i The following tabulated examples illustrate the v01; pement Cham 7. 5 25 5 conditions for simultaneous isomerization of one Com lzlilxlilgs: o l 0 a xylene and separation of the resulting isomeric 1717 ""'f' 411 mixtures by means of HF, BFS liquid, the startz gig 8% ing material being predominately o-xylene in Ex- -o.s 3.3 amples N and O, and m-xylene in Examples P and Q.

Example No N 0 Operating Cbndilionn Temp., F. 150 200 Contact time, min... 60 Press., lbs. gauge 82 132 A prox. We ght percent BF; in HF, BF; 20 R530 riefen-muenster2:: o. l 0.4

Cogli- R f E COI'I R f E posi e a xposi a x- Hydrocarbon distribution Charge prom mme tract Charge prod nte met uct uct Volume Per Cent of Charge.. 78. 6 2l. 4 81. 6 18. 4 Toluene. 0. 1 0.4 5 5 6 a 1 8 Ethylbenzene 0. 7 0. l 0. 4 0. 7

90. 8 43. 1 47.3 27. 8 90. 8 19. 7 2l. 2 l2. 9 6. B 56. 7 43. l 60. 5 6. 8 53. 2 53. 9 49. 9 1. 7 8.7 9. 6 5.1 1. 7 17. 2 1s. 6 10.8 geavier hydrocarbons l. 3 5. 0 4. 5 24. 7

Example No P Q 1st 2nd opmmw Condizione Temp., F- 20o-208 150 150 Contact time, min 10 50 60 Press., ibs. gauge l139 50 52 Approx. weight percent BF: in H kuid 14 About 10-15 Rat o oi' HF, BF; liquid to xyienes.. 0.4 0. 4

Com- R f E Com- R t E posite e. xposte a x- Hydrocsrbon distribution Charge prod mate tract Charge prod mmm tract uct uct Volume percent of Charge.-. 84. 7 15. 3 89. 7 10. 3 Toluene- 0. 2 1. 3 0.1 1. 1 Ethyibenzene. 0. l l. 2 1.2 2. 7 17.0 8.6 1. 2 5.1 5.6 1.1 98.0 64.5 63.0 73.0 98.0 86.6 86.1 90.9 0. 8 18. 4 20. 0 10. 0 0. 8 7. 9 8. 3 4. 2 1.1 7.1 0. 1 1. 3

In Examge P above, the temperature was reduced after 10 minutes to 150 F., and Exam le Q shows that with the H oi 11i-xylene.

, BF; liquid employed a temperature of F. was insuilicient to cause apprecie le isomer-ization 17 In another series o! experiments, isomerlzation and separation of isomers were obtained as iollows:

18 a liquid mixture of HF and BF; in said extraction zone, separating a liquid HF and BF; ex-- tract phase containing selectively extracted di..

Example N o 1 R S T Operating Conditions Temp., "F 75-77 75-80 200 gonmcfbtime' mm 27g 17g 160 ress. s gauge 12 Agprox. w'oight percent BF; in HF,

F1, liqui 24 26 About 2-5 Ratio of HF, BF; liquid to xylenes l (vol. l- 3 1. 3 0. 4 Diluent Propane n-Pentane None Ratio of diluent to xylenes (Vol.) 1. 1. 0

CDH n f F Copil- R 1 E 02,111' R I posi Aa .xposi e a xpo. te af- Ex- Bydrocarbon distribution Charge pmd mmm met Charge pmd nate tract Charge prom mate tract uct uct uct )P701 percent of Charge---- 6i. 5 35. 5 6l. 4 38. 6 0 1 05.1 g Ezhylbenzcne o. a 1.1 1.1 1. 2 o. a 2 2 2. a 'o 0-oxylene. 39. 3 28. 3 40. 6 17:2 39. 3 29. 0 39. 3 l2. 6 1. 2 15. 6 16. 0 9. 3 m-xy1ene 12. 7 26. 0 5. 3 63. 7 12. 7 34. 2 9. 1 74. 0 98. 0 62. 4 '62. 6 58. 1

xylene 47. 7 39. 7 63. 0 15. 4 47- 7 36. 4 5l. 6 12. 3 0. 8 18. 7 19. l 10. 1

eavicr hydrocarbons. 0. 9 2. 5 0. 4 l. l 1. O 20. 0

Itis readily apparent that various modifica-- tions can be made within the spirit of the present invention and scope of the appended claims.

We claim:

1. A process of treating o, mixture of isomeric lower dialkyl benzenes which comprises feeding said mixture to a liquid phase extraction zone, selectively extracting a dialkyl benzene composition isomeric to the mixture of dialkylbenzenes in the feed by contacting said feed with a liquid mixture of HF and BF; in said extraction zone at a temperature not above 100 F., separating a liquid HF and BF3 extract phase containing selectively extracted dialkyl -benzenes from a liquid phase containing undissolved isomeric dialkyl benzenes, the ratio of dialkyl benzene isomers in the extract being materially different from the ratio thereof in said original mixture, and recovering said isomeric dialkyl benzenes from the extract phase. Y.

2. A process of treating a mixture of isomeric lower dialkyl benzenes containing from 1 to 3 carbon atoms inclusive in each alkyl group which comprises feeding said mixture to a liquid phase extraction zone, selectively extracting a. dialkyl benzene composition isomeric to the mixture of dialkyl benzenes in the feed by contacting said feed with a liquid mixture of HF and BF; con- 1 taining in excess of 1% by weight of BF3 in said l lower dialkyl benzenes which comprises diluting said mixture with a volatile lower normal Darain, feeding said diluted mixture to a liquid phase extraction zone, selectively extracting a dialkyl benzene composition isomeric to the mix*- .ture of dialkyl benzenes in the feed by contacting said feed at a temperature not above 100 F. with allnyl benzene compounds from a liquid phaslx containing undissolved isomeric dialkyl benzene compounds, the ratio of dialkyl benzene isomers in the extract being materially different from the ratio thereof in said original mixture, and recovering said isomeric dialkyl benzene compounds from the extract phase.

4. A process for separating a hydrocarbon liquid consisting predominantly ofy lower dialkyl benzene isomers which comprises extracting the hydrocarbon liquid at a, temperature not above about 100 F. with an amount of I-IF-BF3 suiicient to form a distinct phase, but insuilicient to dissolve all of the aromatic hydrocarbons in said liquid whereby an I-IF-BF: vphase enriched in the meta dialkyl benzene isomer is formed.

5., The process as defined in claim 4 wherein the dialkyl benzene isomers are xylenes.

6. A process of separating a xylene mixture containing at least meta and para` xylenes which comprises the steps of contacting said xylene mixture at a temperature not above about 100 F. with a liquid consisting of HF and BF; and containing in excess of 1% by weight of BFs, the ratio of HF-BF3 liquid to xylene mixture being suilicient to form separate layers5 and the xylenes being present in an amount exceeding their substantially complete solubility in the HF- BF: liquid, separating a liquid HF-BF3 extract phase enriched with meta xylene from the immiscible xylene phase, and recovering a. xylene fraction isomeric to the mixture of xylenes in the feed.

7. The process of claim 6, wherein said liquid HF-BF'; mixture contains about 1li-50% by weight of BFa.

8. A process of treating a. fraction of isomeric lower dialkyl benzenes which comprises contacting in at least one step said aromatic fraction with a liquid consisting of HF and BF; at a temperature below about F. and in the presence of a substantially inert diluent immiscible with said HF, BF; liquid, the ratio of HF, BF; liquid to dialkyl benzenes being sumcient to form on settling a separate layer of HF, BFs liquid preferentially enriched with one of said dialkyl benzenes and a separate layer containing the unabsorbed dialkyl benzenes and said diluent, settling and separating said layers. and-thereafter 19 separating the dialkyl benzenes from HF and BF: in at least one of said layers. f

9. The process of claim 8, wherein said diluent is liquid propane.

10. The method of separating meta xylene from a hydrocarbon liquid consisting predominantly of xylene isomers which comprises intimately mixing said hydrocarbon liquid at a temperature not above 'about 100 F. with a selective solvent consisting essentially of HF and BF; and containing at least 10% by weight of BFa in amount suiiicient to form a distinct liquid phase, settling the mixture to separate an upper lwdrocarbon phase and a lower solvent phase enriched in meta, xylene, separating the phases and recovering a hydrocarbon rich in meta xylene from the solvent phase.

1l. An improved process of separating a mixture of ortho, metaand para-xylenes, which comprises the steps of subjecting said mixture to fractionation, whereby ortho-xylene is substantially separated from a. fraction of predominately metaand para-xylenes, contacting said resultant fraction with a liquid consisting of K containing from about l to 50% by weight of BF; at a. temperature below about 80 F., the ratio of mk Blik liquid to xylenes being sufflcient to Ic on settling a separate layer of IF, BF; liquid preferentially enriched with metaxylene and a separate layer containing the major portion of para-miente, settling and separating said layers, removing EF and BF from said layers, and recycling at least a portion of said removed HF and BFa to said contacting step.

l2. The method of separating meta, xylene from a liquid hydrocarbon consisting predominantly of xylene isomers which comprises extracting the liquid hydrocarbons at a temperature'in the range of about 30 F. to 80 F. with an amount of liquid 'm-BF; sufiicient to form a distinct phase, but

insuicient to dissolve all of the aromatic hydrocarbons in the hydrocarbon liquid. separating a rafiinate phase and an extract phase enriched in meta xylene and recovering meta xylene from the extract phase.

13. The method of separating meta xylene from a liquid hydrocarbon mixture consisting predominantly of xylene isomers which comprises extracting the liquid hydrocarbons at a temperature below 100 F. with a volume of HF-BF; less than the volume of the hydrocarbon mixture. but sufiicient lto form a distinct phase, said HF-BF; containing at least 10% by Weight of BFa. separating a railinate phase having a reduced meta xylene content relative to the hydrocarbon mixture and anextract phase comprising HF-BF: and meta xylene, .and separating from the extract phase a hydrocarbon liquid having a high meta xylene content, relative to the hydrocarbon mixture.

14. A process for separating meta xylene from s. liquid hydrocarbon mixture consisting predominantly of xylene isomers which comprises adding from 0.5 to 2.5 volumes of a low boiling parailinic hydrocarbon to 1 volume of the hydrocarbon mixture and extracting the resulting mixture at a temperature below about F. with from 2 to 4 Avolumes of TIF-B2b containing 10 to 50% by weight of BF; to selectively remove meta xylene from the mixture.

LLOYD F. BROOKE. GORDON E. LANGLGIS. ARTHUR E. STICIUJAND.

REFERENCES CITED The following references are of record in the le of this patent:

(Jerticatev of Correction Patent No. 2,521,444

September 5, 195o LLOYD F. BROOKE ET AL.

:it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Coiumn 18, line 26, strike out said feed at a temperature not above F. Wit and insert the same before the Words a 1iqu1d 1n line l, same column;

and that the said Letters Patent should be read as corrected above, so that thesame may conform to the record of the case in the Patent Oice.

Signed and sealed this 14th day of November, A. D. 1950.

' THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

1. A PROCESS OF TREATING A MIXTURE OF ISOMERIC LOWER DIALKYL BENZENES WHICH COMPRISES FEEDING SAID MIXTURE TO A LIQUID PHASE EXTRACTION ZONE, SELECTIVELY EXTRACTING A DIALKYL BENZENE COMPOSITION ISOMERIC TO THE MIXTURE OF DIALKYL BENZENES IN THE FEED BY CONTACTING SAID FEED WITH A LIQUID MIXTURE OF HF AND BF3 IN SAID EXTRACTION ZONE AT A TEMPERTURE NOT ABOVE 100*F., SEPARATING A LIQUID HF AND BF3 EXTRACT PHASE CONTAINING SE- 